The present invention relates to a capacitor and, more particularly, to a capacitor arrangement for filtering noise having a high frequency, such as several tens of mega hertz.
Lead lines for transmitting signals often pick up high frequency noise signals. For example, when the lead line is disposed near a source of a high frequency signal, it picks up the high frequency noise electromagnetically. To eliminate such high frequency noise, a capacitor, such as shown in FIG. 1, is generally connected between the lead line and ground.
The capacitor of FIG. 1 constitutes a ceramic dielectric plate 1, a pair of electrodes 2 and 3 deposited on opposite surfaces of the plate 1, respectively, a pair of terminal legs 4 and 5 extending from the electrodes 2 and 3, respectively, and a synthetic resin coating 6 covering the capacitor for insulation purposes. An equivalent circuit of the capacitor of FIG. 1, when it is connected between the lead line A and ground, is shown in FIG. 2, in which a capacitor C represents capacitance between the electrodes 2 and 3 while inductors L4 and L5 represent inductances of the terminal legs 4 and 5, respectively. When the signals having various frequencies are transmitted through the lead line A, a signal having a certain high frequency is filtered to ground through an L-C filter circuit including the capacitor C and inductors L4 and L5, while the remaining signals are transmitted through the lead line A without any disturbances. The frequency of the signal filtered through the L-C circuit is determined by both the capacitance and inductance between the lead line A and ground. Accordingly, the inductance of the terminal legs 4 and 5 greatly influences the determination of the signal that can be filtered through the L-C circuit. From the view point of practice, the inductance in the L-C circuit should preferably be as low as possible. However, in the capacitor of FIG. 1 the inductors L4 and L5 have such a high inductance that only signals having a considerably low frequency, compared with that of the high frequency noise, are filtered. Therefore, the high frequency noise signals can not be effectively filtered by the capacitor of FIG. 1. Instead, necessary signals (i.e. non-noise signals) may be undesirably filtered to the ground.
To effectively filter the high frequency noise signals, it is necessary to reduce the inductance in the L-C filter circuit. To this end, a capacitor shown in FIG. 3 has been proposed. Instead of the long terminal legs, the capacitor of FIG. 3 has a ribbon-shaped terminal member 7 soldered to the electrode 3, and a screwed terminal member 8 soldered to the other electrode 2. When in use, the screwed terminal member 8 is screwed into a base 9 for grounding the electrode 2 while the ribbon-shaped terminal member 7 is connected in series with the lead line A. Particularly, one wing portion of the ribbon-shaped terminal member 7 is connected to the lead line A' and the other wing portion thereof is connected to a consecutive lead line A". Thereafter, the electrode 3 and a part of the ribbon-shaped terminal member 7 are covered by a synthetic resin 10. An equivalent circuit of the capacitor of FIG. 3 is shown in FIG. 4 in which inductors L7' and L7" represent inductances in the wing portions of the ribbon-shaped terminal member 7 while an inductor L8 represents inductance in the screwed terminal member 8. As understood from the equivalent circuit of FIG. 4, the L-C filter circuit is defined by the capacitor C and the inductor L8. The inductors L7' and Ll7" serve as inductive impedances in the successive lead lines A' and A". Thus, the L-C filter presents a considerably low inductance and thereby effectively filters the high frequency noise signals in line A.
Although the capacitor of FIG. 3 effectively eliminates high frequency noise signals, it is costly to manufacture because of the particular shaped terminal members and its time consuming task for the installation. Furthermore, it occupies a large space when it is installed in a device.
Accordingly, a primary object of the present invention is to provide a capacitor arrangement which effectively filters high frequency noises.
It is another object of the present invention to provide a capacitor arrangement of the above described type which is simple in construction and can readily be manufactured at low cost.